Drain pump assembly for a dishwasher appliance

ABSTRACT

A dishwasher appliance is provided having a sump for collecting wash fluid and a drain pump assembly for discharging wash fluid. The sump defines a drain basin and a drain cover is positioned over the drain basin to define a drain volute. A drain pump impeller is positioned within the drain volute on a drive shaft driven by a motor in a first direction during a wash cycle and in an opposite second direction during a drain cycle. During the wash cycle, soil enters the drain volute through a suction inlet defined by the drain cover where it is urged radially outward and trapped within the drain basin. When the motor operation is reversed, the drain pump impeller discharges the soiled wash fluid from the drain volute through a discharge conduit.

FIELD OF THE INVENTION

The present disclosure relates generally to dishwasher appliances, and more particularly to an improved drain pump assembly for dishwasher appliances.

BACKGROUND OF THE INVENTION

Dishwasher appliances generally include a tub that defines a wash chamber. Rack assemblies can be mounted within the wash chamber of the tub for receipt of articles for washing. Wash fluid (e.g., various combinations of water and detergent along with optional additives) may be introduced into the tub where it collects in a sump space at the bottom of the wash chamber. During wash and rinse cycles, a pump may be used to circulate wash fluid to spray assemblies within the wash chamber that can apply or direct wash fluid towards articles disposed within the rack assemblies in order to clean such articles. During a drain cycle, a pump may periodically discharge soiled wash fluid that collects in the sump space and the process may be repeated.

Conventional dishwasher appliances use two separate motors to operate a wash pump and a drain pump. However, additional motors take up more space, add cost, and require additional seals, thus increasing the likelihood of leaks and decreasing appliance reliability. Certain dishwasher appliances have eliminated the need for a second motor by using a single motor and a common drive shaft to rotate a wash pump impeller and a drain pump impeller. In this regard, the wash pump impeller and the drain pump impeller may be separated by a filter, and the motor may rotate in one direction to circulate wash fluid (i.e., the “wash direction”) and the other to drain wash fluid (i.e., the “drain direction”).

Because impellers have the tendency to pump fluid even when rotated in the reverse direction (albeit less efficiently), soil collected in the bottom of the sump may be churned or agitated during the wash cycle. However, cleaning efficiency and dishwasher operation is improved when food particles and soil are removed from the wash fluid circulating in the wash chamber. Certain dishwasher appliances have attempted to remove soils using complicated filtering systems, but these solutions may be expensive and/or not effective for containing such soils.

Accordingly, a dishwasher appliance that utilizes an improved drain pump assembly would be useful. More specifically, a drain pump assembly that collects or traps soils when the drive shaft is rotated in the wash direction would be particularly beneficial.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a dishwasher appliance having a sump for collecting wash fluid and a drain pump assembly for discharging wash fluid. The sump defines a drain basin and a drain cover is positioned over the drain basin to define a drain volute. A drain pump impeller is positioned within the drain volute on a drive shaft driven by a motor in a first direction during a wash cycle and in an opposite second direction during a drain cycle. During the wash cycle, soil enters the drain volute through a suction inlet defined by the drain cover where it is urged radially outward and trapped within the drain basin. When the motor operation is reversed, the drain pump impeller discharges the soiled wash fluid from the drain volute through a discharge conduit. Additional aspects and advantages of the invention will be set forth in part in the following description, may be apparent from the description, or may be learned through practice of the invention.

In accordance with one exemplary embodiment of the present disclosure, a drain pump assembly for a dishwasher appliance is provided. The drain pump assembly includes a sump for collecting wash fluid, the sump defining a drain basin proximate a bottom of the sump. A drain cover is positioned over the drain basin to define a drain volute, the drain cover defining a suction inlet to the drain volute. A drive shaft defines an axial direction and a radial direction perpendicular to the axial direction, the drive shaft extending through the suction inlet into the drain volute. A motor is operable to rotate the drive shaft in a first direction during a wash cycle and in a second direction during a drain cycle, the second direction being opposite the first direction. A drain pump impeller is positioned within the drain volute and coupled to the drive shaft.

In accordance with another exemplary embodiment of the present disclosure, a dishwasher appliance defining a vertical direction is provided. The dishwasher appliance includes a wash tub that defines a wash chamber and a sump for collecting wash fluid. A drive shaft defines an axial direction and a radial direction perpendicular to the axial direction. A motor is operable to rotate the drive shaft in a first direction during a wash cycle and in a second direction during a drain cycle, the second direction being opposite the first direction. A wash pump impeller is coupled to the drive shaft for providing a flow of wash fluid for cleaning articles placed within the wash chamber when the motor rotates in the first direction. The dishwasher further includes a drain pump assembly including a drain basin positioned proximate a bottom of the sump and a drain cover positioned over the drain basin to define a drain volute, the drain cover defining a suction inlet to the drain volute. A drain pump impeller is positioned within the drain volute and coupled to the drive shaft for discharging wash fluid when the motor rotates in the second direction.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 provides a front view of an exemplary embodiment of a dishwashing appliance of the present disclosure.

FIG. 2 provides a side, cross sectional view of the exemplary dishwashing appliance of FIG. 1.

FIG. 3 provides a side, cross sectional view of a fluid circulation assembly according to an example embodiment of the present subject matter.

FIG. 4 provides a cross sectional view of a drain pump assembly of the exemplary fluid circulation assembly of FIG. 3 according to an exemplary embodiment of the present subject matter.

FIG. 5 provides another cross sectional view of the exemplary drain pump assembly of FIG. 4 according to an example embodiment of the present subject matter.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

As used herein, the term “article” may refer to, but need not be limited to dishes, pots, pans, silverware, and other cooking utensils and items that can be cleaned in a dishwashing appliance. The term “wash cycle” is intended to refer to one or more periods of time during which a dishwashing appliance operates while containing the articles to be washed and uses a detergent and water, preferably with agitation, to e.g., remove soil particles including food and other undesirable elements from the articles. The term “rinse cycle” is intended to refer to one or more periods of time during which the dishwashing appliance operates to remove residual soil, detergents, and other undesirable elements that were retained by the articles after completion of the wash cycle. The term “drain cycle” is intended to refer to one or more periods of time during which the dishwashing appliance operates to discharge soiled water from the dishwashing appliance. The term “wash fluid” refers to a liquid used for washing and/or rinsing the articles and is typically made up of water that may include other additives such as detergent or other treatments.

FIGS. 1 and 2 depict an exemplary domestic dishwasher or dishwashing appliance 100 that may be configured in accordance with aspects of the present disclosure. For the particular embodiment of FIGS. 1 and 2, the dishwasher 100 includes a cabinet 102 having a tub 104 therein that defines a wash chamber 106. As shown in FIG. 2, the tub extends between a top 107 and a bottom 108 along a vertical direction V, between a first side and a second side along a lateral direction L, and between a front side 111 and a rear side 112 along a transverse direction T. Each of the vertical direction V, lateral direction L, and transverse direction T are mutually perpendicular to one another. The tub 104 includes a front opening (not shown) and a door 114 hinged at its bottom 116 for movement between a normally closed vertical position (shown in FIGS. 1 and 2), wherein the wash chamber 106 is sealed shut for washing operation, and a horizontal open position for loading and unloading of articles from the dishwasher 100. Latch 118 is used to lock and unlock door 114 for access to wash chamber 106.

Upper and lower guide rails 120, 122 are mounted on the first and second sides of tub 104 and accommodate roller-equipped rack assemblies 126 and 128. Each of the rack assemblies 126, 128 is fabricated into lattice structures including a plurality of elongated members 130 (for clarity of illustration, not all elongated members making up assemblies 126 and 128 are shown in FIG. 2). Each rack 126, 128 is adapted for movement between an extended loading position (not shown) in which the rack is substantially positioned outside the wash chamber 106, and a retracted position (shown in FIGS. 1 and 2) in which the rack is located inside the wash chamber 106. This is facilitated by rollers 134 and 136, for example, mounted onto racks 126 and 128, respectively. A silverware basket (not shown) may be removably attached to rack assembly 128 for placement of silverware, utensils, and the like, that are otherwise too small to be accommodated by racks 126, 128.

The dishwasher 100 further includes a lower spray arm assembly 140 that will be described in more detail below. Lower spray arm assembly 140 may be disposed in a lower region 142 of the wash chamber 106 and above a tub sump 144 so as to rotate in relatively close proximity to rack assembly 128. A mid-level spray arm assembly 146 is located in an upper region of the wash chamber 106 and may be located in close proximity to upper rack 126. Additionally, an upper spray assembly 148 may be located above the upper rack 126. As will be described in detail below, spray arm assemblies 140, 146, 148 may be part of a fluid circulation assembly 150 for circulating water and dishwasher fluid in the tub 104.

Each spray arm assembly 140, 146, 148 includes an arrangement of discharge ports or orifices for directing washing liquid received from fluid circulation assembly 150 onto dishes or other articles located in rack assemblies 126 and 128. The arrangement of the discharge ports, also referred to as jets, apertures, or orifices, may provide a rotational force by virtue of washing fluid flowing through the discharge ports. Alternatively, spray arm assemblies 140, 146, 148 may be motor-driven, or may operate using any other suitable drive mechanism. The resultant movement of the spray arm assemblies 140, 146, 148 provides coverage of dishes and other dishwasher contents with a washing spray. Other configurations of spray assemblies may be used as well. For example, dishwasher 100 may have additional spray assemblies for cleaning silverware, for scouring casserole dishes, for spraying pots and pans, for cleaning bottles, etc. One skilled in the art will appreciate that the embodiments discussed herein are used for the purpose of explanation only, and are not limitations of the present subject matter.

The dishwasher 100 is further equipped with a controller 156 to regulate operation of the dishwasher 100. The controller 156 may include one or more memory devices and one or more microprocessors, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor.

The controller 156 may be positioned in a variety of locations throughout dishwasher 100. In the illustrated embodiment, the controller 156 may be located within a control panel area 158 of door 114 as shown in FIGS. 1 and 2. In such an embodiment, input/output (“I/O”) signals may be routed between the control system and various operational components of dishwasher 100 along wiring harnesses that may be routed through the bottom 116 of door 114. Typically, the controller 156 includes a user interface panel/controls 160 through which a user may select various operational features and modes and monitor progress of the dishwasher 100. In one embodiment, the user interface 160 may represent a general purpose I/O (“GPIO”) device or functional block. In one embodiment, the user interface 160 may include input components, such as one or more of a variety of electrical, mechanical or electro-mechanical input devices including rotary dials, push buttons, and touch pads. The user interface 160 may include a display component, such as a digital or analog display device designed to provide operational feedback to a user. The user interface 160 may be in communication with the controller 156 via one or more signal lines or shared communication busses.

It should be appreciated that the invention is not limited to any particular style, model, or configuration of dishwasher 100. The exemplary embodiment depicted in FIGS. 1 and 2 is for illustrative purposes only. For example, different locations may be provided for user interface 160, different configurations may be provided for racks 126, 128, different spray arm assemblies 140, 146, 148 may be used, and other differences may be applied as well.

Referring now generally to FIG. 3, a fluid circulation assembly 150 according to an example embodiment of the present subject matter will be described. Fluid circulation assembly 150 may include a drive motor 170 that may be disposed within sump 144 of tub 104 and may be configured to rotate multiple components of dishwasher 100. As best shown in FIG. 3, drive motor 170 may be, for example, a brushless DC motor having a stator 172, a rotor 174, and a drive shaft 176 attached to rotor 174. A controller or control board (not shown) may control the speed of motor 170 and rotation of drive shaft 176 by selectively applying electric current to stator 172 to cause rotor 174 and drive shaft 176 to rotate. Although drive motor 170 is illustrated herein as a brushless DC motor, it should be appreciated that any suitable motor may be used while remaining within the scope of the present subject matter. For example, according to alternative embodiments, drive motor 170 may instead be a synchronous permanent magnet motor.

According to an example embodiment, drive motor 170 may be a variable speed motor. In this regard, drive motor 170 may be operated at various speeds depending on the current operating cycle of the dishwasher. For example, according to an exemplary embodiment, drive motor 170 may be configured to operate at any speed between a minimum speed, e.g., 1500 revolutions per minute (RPM), to a maximum rated speed, e.g., 4500 RPM. In this manner, use of a variable speed drive motor 170 enables efficient operation of dishwasher 100 in any operating mode. Thus, for example, the drain cycle may require a lower rotational speed than a wash cycle and/or rinse cycle. A variable speed drive motor 170 allows impeller rotation at the desired speeds while minimizing energy usage and unnecessary noise when drive motor 170 does not need to operate at full speed.

According to an exemplary embodiment, drive motor 170 and all its components may be potted. In this manner, drive motor 170 may be shock-resistant, submersible, and generally more reliable. Notably, because drive motor 170 is mounted inside wash chamber 106 and is completely submersible, no seals are required and the likelihood of leaks is reduced. In addition, because drive motor 170 is mounted in the normally unused space between lower spray arm 140 and a bottom wall of sump 144, instead of beneath the sump 144, this design is inherently more compact than conventional designs.

According to an exemplary embodiment, fluid circulation assembly 150 may be vertically mounted within sump 144 of wash chamber 106. More particularly, drive motor 170 of fluid circulation assembly 150 may be mounted such that drive shaft 176 is oriented along vertical direction V of dishwasher 100. More particularly, drive shaft 176 may define an axial direction A, a radial direction R, and a circumferential direction C (FIG. 4), with the axial direction A being parallel to the vertical direction V of the dishwasher 100. As illustrated in FIG. 3, drive shaft 176 is rotatably supported by upper and lower bearings and extends out of a bottom of drive motor 170 toward a bottom of sump 144.

Referring now to FIGS. 3 and 4, drive shaft 176 is configured for driving a circulation or wash pump assembly 180. Wash pump assembly 180 may generally be configured for circulating wash fluid within wash chamber 106 during wash and/or rinse cycles. More specifically, wash pump assembly 180 may include a wash pump impeller 182 disposed on drive shaft 176 within a pump housing 184. Pump housing 184 defines a pump intake 186 for drawing wash fluid into wash pump impeller 182. According to the illustrated embodiment, pump intake 186 is facing downward along the vertical direction V and is located very near the bottom of sump 144. In this manner, the amount of water required to prime and operate wash pump assembly 180 is minimized. This is particularly advantageous when running low water cycles for the purpose of water and energy savings.

In operation, wash pump impeller 182 draws wash fluid in from sump 144 and pumps it to a diverter assembly 190. Diverter assembly 190 may include a diverter disc 192 disposed within a diverter chamber 194 for selectively distributing the wash fluid to the spray arm assemblies 140, 146, 148. More particularly, diverter disc 192 may be rotatably mounted about the vertical direction V. Diverter disc 192 may have a plurality of apertures that are configured to align with a one or more outlet ports at the top of diverter chamber 194. In this manner, diverter disc 192 may be selectively rotated to provide wash fluid to spray arm assemblies 140, 146, 148.

As illustrated in FIG. 3, fluid circulation assembly 150 further includes a filter 196. In general, filter 196 may define an unfiltered region 197 and a filtered region 198 within sump 144. During a wash or rinse cycle, wash fluid sprayed on dishes or other articles within wash chamber 106 falls into the unfiltered region 197. Wash fluid passes through filter 196 which removes food particles, resulting in relatively clean wash fluid within the filtered region 198. As used herein, “food particles” refers to food soil, particles, sediment, or other contaminants in the wash fluid which are not intended to travel through filter 196. Thus, a food particle seal may allow water or other wash fluids to pass from the unfiltered region 197 to the filtered region 198 while preventing food particles entrained within that wash fluid from passing along with the wash fluid.

As illustrated, filter 196 is a cylindrical and conical fine mesh filter constructed from a perforated stainless steel plate. Filter 196 may include a plurality of perforated holes, e.g., approximately 15/1000 of an inch in diameter, such that wash fluid may pass through filter 196, but food particles entrained in the wash fluid do not pass through filter 196. However, according to alternative embodiments, filter 196 may be any structure suitable for filtering food particles from wash fluid passing through filter 196. For example, filter 196 may be constructed from any suitably rigid material, may be formed into any suitable shape, and may include apertures of any suitable size for capturing particulates.

According to the illustrated exemplary embodiment, filter 196 defines an aperture through which drive shaft 176 extends. Wash pump impeller 182 is coupled to drive shaft 176 above filter 196 and a drain pump assembly (e.g., as described below) is coupled to drive shaft 176 below filter 196 along the vertical direction V. Fluid circulation assembly 150 may further include an inlet guide assembly 199 which is configured for accurately locating and securing filter 196 while allowing drive shaft 176 to pass through aperture and minimizing leaks between the filtered and unfiltered regions 197, 198 of sump 144. More specifically, as best illustrated in FIG. 5, drive shaft 176 passes through a clearance bore in inlet guide assembly 199 and through filter 196 between unfiltered region 197 and filtered region 198 of sump 144. Because the clearance bore has a diameter that is larger than the diameter of drive shaft 176, inlet guide assembly 199 may further include a washer disposed within a chamber, e.g., in order to accommodate minor drive shaft wobble or misalignment while retaining a particle tight seal.

Referring now generally to FIGS. 3 through 5, a drain pump assembly 200 according to an exemplary embodiment of the present subject matter will be described. Drain pump assembly 200 may generally be configured for periodically discharging soiled wash fluid from dishwasher 100. Although illustrated and described as part of fluid circulation assembly 150, it should be appreciated that aspects of drain pump assembly 200 may be used in any impeller assembly in any application where it is desirable to selectively pump a fluid. In this regard, drain pump assembly 200 is only one exemplary configuration used for the purpose of explaining aspects of the present subject matter and is not intended to limit the scope of the invention in any manner.

Drain pump assembly 200 may include a drain pump impeller 202 coupled to a bottom portion of drive shaft 176 and positioned within a drain volute 204 below filter 196. More specifically, drain volute 204 is defined by a drain basin 206 of sump 144 and a drain cover 208. In this regard, according to the exemplary embodiment, drain basin 106 defines a bottom wall 210 and a cylindrical side wall 212 of sump 144. Drain cover 208 is positioned over drain basin 206 and forms a fluid tight seal with side wall 212, e.g., by using an O-ring 214 or any other suitable sealing mechanism. According to the illustrated embodiment, the bottom of sump 144 and drain cover 208 define a seamless transition and are cone-shaped to help funnel food particles toward drain volute 202. For example, as illustrated, sump 144 and drain cover 208 define a frustum of a cone above drain basin 206.

As best shown in FIG. 5, drain pump assembly 200 further includes a discharge conduit 216 in fluid communication with drain volute 204. According to the illustrated embodiment discharge conduit 216 extends from drain basin 206 substantially perpendicular to the radial direction R. In other words, discharge conduit 216 is oriented substantially tangentially to vanes 224 of drain pump impeller 202. It should be appreciated, that as used herein, terms of approximation, such as “about” or “approximately,” refer to being within a 10% margin of error.

Drain cover 208 defines a suction inlet 220 through which wash fluid may pass into drain volute 204. As illustrated, suction inlet 220 is a circular aperture in the center of drain cover 208, but other sizes and geometries may be used according to alternative embodiments. As illustrated drive shaft 176 passes through suction inlet 220 into drain volute 204 where it is coupled to drain pump impeller 202. More specifically, drain pump impeller 202 generally includes a hub 222 that is mounted to drive shaft 176. Hub 222 has a circular bore that is configured for receiving a bottom end of drive shaft 176. In an embodiment, drive shaft 176 and hub 222 may be keyed so as to be in cooperative engagement. In this regard, for example, drive shaft 176 may include one or more features, such as protrusions (not shown), in cooperative engagement with one or more features, such as recesses (not shown), in hub 222, or vice versa. In addition, one or more pins, retaining clips, or other mechanical retention devices may be used to fix hub 222 to drive shaft 176.

Notably, drain pump impeller 202 is coupled to the bottom portion of drive shaft 176 using a one-way clutch 226. In this regard, during a wash/rinse cycle, drive motor 170 rotates in one direction, pumping filtered wash fluid using wash pump impeller 182. However, one-way clutch 226 is disengaged, so drain pump impeller 202 does not rotate at the same speed. Instead, drain pump impeller 202 may rotate at a decreased speed, e.g., due to some friction between one-way clutch 226 and drive shaft 176. According to alternative embodiments, drain pump impeller 202 may remain stationary during the wash cycle or may rotate at the same speed as wash pump impeller 182. In both cases, soil and food particles will have a tendency to collect within drain volute 204, as described herein. By contrast, during a drain cycle, drive motor 170 rotates in the opposite direction, thereby engaging one-way clutch 226 and causing drain pump impeller 202 to rotate and discharge wash fluid.

Drain pump impeller 202 may further includes a plurality of vanes 224 that extend from hub 222 for pumping wash fluid. Vanes 224 may extend from a root 230 proximate hub 222 to a tip 232 substantially along the radial direction R. In addition, vanes 224 may be straight, curved, or any other suitable shape for achieve the desired pumping action and pressure heads when drain pump impeller 202 is rotated.

In general, drain volute 204 is oversized relative to drain pump impeller 202 to accommodate large food particles or other food soil that is drawn into drain volute 204. In this regard, the size of drain volute 204 relative to drain pump impeller 202 may be manipulated as desired depending on the application. For example, as best shown in FIG. 5, a radial gap 234 is defined between drain pump impeller 202 and drain basin 206 along the radial direction R. More specifically, for example, radial gap 234 may be defined between tip 232 of each vane 224 and side wall 212 of drain basin 206. As drain pump impeller 202 rotates, vanes 224 urge such food particles radially outward to radial gap 234 where they are pinned or otherwise trapped within drain volute 204 adjacent side wall 212 until the next drain cycle.

According to the exemplary embodiment, drain volute 204 defines a first diameter 240 and drain pump impeller 202 defines a second diameter 242. According to example embodiments, first diameter 240 is larger than second diameter 242. In this regard, first diameter 240 may be about five percent, ten percent, or greater than twenty percent larger than second diameter 242, e.g., to accommodate a larger size or quantity of food particles. In addition, to allow food particles to flow within drain volute 204 without binding between drain pump impeller 202 and drain basin 206 or drain cover 208, a vertical gap 244 may be defined between a top of drain pump impeller 202 and the drain cover 208.

As illustrated, suction inlet 220 is positioned at a center of drain cover 208 and is sized such that wash fluid and large food particles may pass into drain volute 204. However, drain cover 208 also acts as a barrier to prevent soil that collects around a perimeter of drain volute 204 from escaping drain volute 204, e.g., along the vertical direction V. In this manner, as drain pump impeller 202 rotates, soil and food particles are urged toward side wall 212 of drain basin 206 where they are trapped and collect until a drain cycle is initiated. When drive shaft 176 is rotated in the drain direction, wash fluid and soils collected in drain volute 204 are quickly and efficiently expelled through discharge conduit 216.

Drain pump volute 202 and discharge conduit 216 are both positioned at the very bottom of sump 144, at the lowest portion of fluid circulation assembly 150, providing several operational advantages. Specifically, heavier soil tends to fall toward drain volute 204 where wash fluid and food particles are collected. During a drain cycle, drain pump impeller 202 is rotated and soiled wash fluid is discharged from dishwasher 100 through a discharge conduit 216 such that complete draining of soiled wash fluid may be achieved. After some or all of the soiled wash fluid is discharged, fresh water and/or wash additives may be added and the wash or rinse cycle may be repeated.

It should be appreciated that drain pump assembly 200 is used only for the purpose of explaining aspects of the present subject matter. Modifications and variations may be made to drain pump assembly 200 while remaining within the scope of the present subject matter. For example, the number, size, spacing, and configuration of vanes 224 may be adjusted while remaining within the scope of the present subject matter. In addition, other embodiments may use more than four vanes having variable lengths, the vanes may have a different number and/or size of links, a different hinge configuration may be used, and biasing members may have a different size or configuration.

Drain pump assembly 200 as described above enables both a wash pump impeller and a drain pump impeller of a dishwasher fluid circulation system to be placed on a single drive shaft. In this manner, a single, reversible drive motor can rotate the drive shaft in a first direction for wash/rinse cycles and in the opposite direction for drain cycles. Furthermore, because the drain pump impeller rotates relatively slowly during the wash cycle, the drain pump impeller draws food particles and soil into the drain pump volute and urges it radially outward to trap it in the drain volute. In this manner, wash fluid circulated within the wash chamber has a lower soil content and can facilitate more effective cleaning of articles placing in the dishwashing racks. In addition, the soil is trapped or contained proximate a discharge conduit for effective discharge when the drain pump impeller is rotated in the drain direction.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A drain pump assembly for a dishwasher appliance, the drain pump assembly comprising: a sump for collecting wash fluid, the sump defining a drain basin proximate a bottom of the sump; a drain cover positioned over the drain basin to define a drain volute, the drain cover defining a suction inlet to the drain volute; a drive shaft defining an axial direction and a radial direction perpendicular to the axial direction, the drive shaft extending through the suction inlet into the drain volute; a motor operable to rotate the drive shaft in a first direction during a wash cycle and in a second direction during a drain cycle, the second direction being opposite the first direction; and a drain pump impeller positioned within the drain volute and coupled to the drive shaft.
 2. The drain pump assembly of claim 1, further comprising a discharge conduit in fluid communication with the drain volute.
 3. The drain pump assembly of claim 2, wherein the discharge conduit extends from the drain basin substantially perpendicular to the radial direction.
 4. The drain pump assembly of claim 1, wherein a radial gap is defined between the drain pump impeller and the drain basin along the radial direction.
 5. The drain pump assembly of claim 4, wherein the drain volute defines a first diameter and the drain pump impeller defines a second diameter, the first diameter being about ten to fifty percent larger than the second diameter.
 6. The drain pump assembly of claim 1, wherein the drain pump impeller is coupled to the drive shaft using a one-way clutch.
 7. The drain pump assembly of claim 1, wherein the motor is a variable speed motor.
 8. The drain pump assembly of claim 7, wherein the variable speed motor is configured for rotating drive shaft at a first speed when rotating in the first direction and a second speed when rotating in the second direction, the second speed being slower than the first speed.
 9. The drain pump assembly of claim 1, wherein a vertical gap is defined between a top of the drain pump impeller and the drain cover.
 10. The drain pump assembly of claim 1, wherein the sump and the drain cover define a frustum of a cone above the drain basin.
 11. The drain pump assembly of claim 1, wherein the motor is vertically oriented within a sump area of the dishwasher appliance, such that the drive shaft is vertically oriented relative to the dishwasher appliance.
 12. A dishwasher appliance defining a vertical direction, the dishwasher appliance comprising: a wash tub that defines a wash chamber; a sump for collecting wash fluid; a drive shaft defining an axial direction and a radial direction perpendicular to the axial direction; a motor operable to rotate the drive shaft in a first direction during a wash cycle and in a second direction during a drain cycle, the second direction being opposite the first direction; a wash pump impeller coupled to the drive shaft for providing a flow of wash fluid for cleaning articles placed within the wash chamber when the motor rotates in the first direction; and a drain pump assembly comprising: a drain basin positioned proximate a bottom of the sump; a drain cover positioned over the drain basin to define a drain volute, the drain cover defining a suction inlet to the drain volute; and a drain pump impeller positioned within the drain volute and coupled to the drive shaft for discharging wash fluid when the motor rotates in the second direction.
 13. The dishwasher appliance of claim 12, further comprising a discharge conduit in fluid communication with the drain volute.
 14. The dishwasher appliance of claim 13, wherein the discharge conduit extends from the drain basin substantially perpendicular to the radial direction.
 15. The dishwasher appliance of claim 12, wherein a radial gap is defined between the drain pump impeller and the drain basin along the radial direction.
 16. The dishwasher appliance of claim 15, wherein the drain volute defines a first diameter and the drain pump impeller defines a second diameter, the first diameter being about ten percent larger than the second diameter.
 17. The dishwasher appliance of claim 12, wherein the drain pump impeller is coupled to the drive shaft using a one-way clutch.
 18. The dishwasher appliance of claim 12, wherein the motor is a variable speed motor.
 19. The dishwasher appliance of claim 12, wherein a vertical gap is defined between a top of the drain pump impeller and the drain cover.
 20. The dishwasher appliance of claim 12, wherein the sump and the drain cover define a frustum of a cone above the drain basin. 